This invention relates to laundry machines, and more particularly, to automatic clothes washers that have a system for controlling the temperature of water introduced into the washing machine tub.
Regulating the temperature of water introduced into an automatic washing machine by controlling the operation of the hot and cold water supply valves of the washing machine is well known. Typically, in prior art machines, a temperature responsive switch, such as a thermostat, is used to sense the temperature of the mixed water entering the tub. The output of the thermostat is applied through appropriate control circuit means to control the opening and closing of the hot and cold water valves to achieve an incoming mixed water temperature which is intended to approximate a desired temperature setting which has been inserted by the user by means of a switch mounted on the control panel of the washing machine.
One such typical arrangement that has been utilized is shown in U.S. Pat. No. 2,533,624 and in U.S. Pat. No. 2,619,284 which show the use of a thermostat located in the washing machine tub. Such arrangements, however, result in some rather basic difficulties. In most automatic washing machines, there is a water level control for use with large or small wash loads. With such an arrangement, the thermostat does not have a fixed ideal location on the tub for different selected water fill levels. For instance, if the thermostat is located to enable sensing with low water fill levels, it is then unable to measure accurately the incoming water when high water fill levels are used. Conversely, a thermostat placed high on the tub obviously is not able to sense water temperature when small water loads are employed.
Another arrangement is disclosed in U.S. Pat. No. 2,844,320 wherein the water valves are controlled by a thermostat located along a mutual output water line or a mixing chamber prior to entry of the water into the washing machine tub. Such an arrangement, however, has been found to detrimentally affect both the thermostat and the water valves due to excessive on and off cycling caused by rapid changes in the water temperature occurring in the output water line. In U.S. Pat. No. 4,031,911, this problem is alleviated somewhat by use of a bypass water sampling tank with a pair of thermostatic switches to hold the water introduced into the tub within a temperature range determined by the trip temperatures of the respective thermostatic switches. Although useful for its intended purpose, it nonetheless relies on electromechanical switch devices and a special sampling chamber for its operation. It is desirable that static temperature sensor arrangements be used for greater reliability. Also it is desirable that special sampling chambers be avoided in order to minimize product cost. It is further desirable to provide an improved form of water temperature control that permits greater flexibility in the choice of wash water temperatures best suited to the various synthetic fabrics now commonly in use.